Secure Relay Beamforming for Simultaneous Wireless Information and Power Transfer in Nonregenerative Relay Networks

For simultaneous wireless information and power transfer (SWIPT), secure communication is an important issue. In this correspondence, we study the secure relay beamforming (SRB) scheme for SWIPT in a nonregenerative multiantenna relay network. We propose a constrained concave convex procedure (CCCP)-based iterative algorithm that is able to achieve a local optimum, where the secrecy rate is maximized, and the relay transmit power and energy harvesting constraints are satisfied. Simulation results have shown that our proposed CCCP-based iterative algorithm achieves a larger secrecy rate and lower computational complexity than the convectional SRB schemes. Since the CCCP-based iterative algorithm is still complex, we propose a semidefinite programming (SDP)-based noniterative suboptimal algorithm and a closed-form suboptimal algorithm. It is shown that when the maximum transmit power of the relay to noise power ratio is high, the SDP-based noniterative suboptimal algorithm performs close to the CCCP-based iterative algorithm.